Early communications satellites were used as dumb repeaters operating in a bent-pipe mode. Initially, no significant processing was carried in the satellite payload other than frequency translation and signal amplification and the information relayed to the destination was fundamentally identical to the information from the source. Multibeam satellites operating in the bent-pipe mode were then introduced. These multibeam satellites relayed messages from one or more sources to several destinations. However, the architecture of these multibeam satellites allowed limited flexibility in selecting between input sources and output destinations. Typical were the first broadcast satellites that relayed information to several geographic destinations.
Multibeam satellites having on-board switching capability were then introduced. In these satellites, incoming beams from a source carry several frequency-multiplexed channels. A typical satellite having on-board switching capability includes an input demultiplexer near the front end of the satellite. The input demultiplexer separates the incoming beams into transponder channels. These channels are then interbeam switched by means of coaxial switches so that information arriving from one of the incoming beams can be directed to one of several output beams.